Tpl2调节爆发性肝炎的病理与分子机制研究

Fulminant hepatitis has a high mortality rate, but its pathological mechanism still remains elusive. Recently, it was reported that IL-25 (IL-17E), which is highly and constitutively expressed in liver, could inhibit inflammatory responses and protect against liver injury during FH pathology. The applicant previously found that the protein kinase Tpl2 could regulate IL-17A-mediated signal transduction, leading to the development of autoimmune inflammation. Due to IL-25 and IL-17A both belong to IL-17 family member, we speculate that Tpl2 may also regulate IL-25-mediated signal transduction, and affect the pathogenesis of FH. Based on the preliminary results, which is MDSC recruitment to inflammatory liver is significantly reduced in Tpl2-deficient mice, leading to promoted mortality rate. Taking advantage of the Tpl2-deficient mice, the applicant will further investigate the role of Tpl2 in the regulation of FH pathology, elucidate the molecular mechanism that induce MDSC recruitment to inflammatory liver, and figure out how Tpl2 regulate IL-25-mediated signal transduction. In addition, the applicant will further develop Tpl2-targeted immune preventive and therapeutic strategy to FH, and provide novel theory and cure approach for FH clinical treatment.

爆发性肝炎（Fulminant hepatitis, FH）致死率高，然而其病理机制仍不甚清楚，目前缺乏有效的治疗手段。近年发现，肝脏中组成型高表达的IL-25（IL-17E）在FH中起到了抑炎与护肝的作用。申请者此前发现蛋白激酶Tpl2可通过调节IL-17A信号通路，并影响机体自身免疫性炎症的发生，因此推测Tpl2同样可以调节同家族的IL-25介导的信号通路，并影响FH的病理进程。为此在前期工作基础上，即Tpl2缺失后减少了MDSC向炎症肝脏的招募，使得FH诱导的小鼠死亡率更高。拟进一步利用Tpl2基因敲除小鼠研究Tpl2在FH病理过程中的作用机制，解析其调节MDSC向炎症性肝脏招募的分子机理，并阐明Tpl2在调节IL-25介导的信号通路转导的分子机制。在此基础上，开发形成以Tpl2为特异性靶向的针对FH的免疫防治新策略，并为其临床治疗提供新的理论基础和防治手段。

炎症微环境中的免疫细胞包括巨噬细胞、中性粒细胞和T、B淋巴细胞等，其中T细胞介导的细胞免疫是导致暴发性肝炎（fulminant hepatitis，FH）引起肝损伤的主要原因，而骨髓来源的抑制性细胞（myeloid-derived suppressor cells，MDSC）在抑制此过程中发挥重要的调控作用。本项目发现Tpl2缺失引起IL-25诱导的肝脏实质细胞基因表达谱的变化，结合小鼠体内实验，充分证明在肝脏实质细胞中Tpl2调节IL-25（也被称为IL-17E）信号通路，并促进趋化因子CXCL1和CXCL2在肝脏实质细胞中的表达和分泌，进而介导招募MDSC向肝脏组织迁移，导致炎症肝脏组织中MDSC靶向抑制浸润的致病CD4+ T细胞的增殖，从而保护肝脏组织免于炎症诱导的急性肝衰竭。该项目证明了Tpl2作为关键调控因子介导MDSC向肝脏招募，进而在FH中发挥重要作用的病理机制。此外，本项目还深入的探究了炎症微环境中巨噬细胞在调节机体自身免疫性炎症的关键作用机理，发现组蛋白甲基转移酶Ezh2可通过介导H3K27三甲基化直接靶向抑制巨噬细胞中SOCS3的表达，从而有效的促进TRAF6的蛋白稳定性，并激活TLR诱导的下游NF-κB信号通路的活化，促炎症细胞因子的表达，最终参与了自身免疫性炎症病理的发生发展。还揭示了炎症微环境中，E3泛素连接酶Peli1通过负调节非经典NF-κB信号通路以抑制B细胞的自身抗体的产生与系统性红斑狼疮的发病机制。本项目通过聚焦炎性微环境，阐明了T细胞、巨噬细胞以及B细胞在炎症相关疾病中的调控机制，丰富与完善了相关炎症性疾病致病机制的理论知识，为相关疾病的诊断与治疗提供了新的潜在分子靶标与治疗策略。